Estrogen is a type of sex hormone classified as a steroid hormone, and is called an estrogenic hormone or a female hormone. Estrogen is produced in the ovaries, transported around the body, and binds to estrogen receptors in the cytoplasm. The estrogen-bound receptor translocates into the nucleus, and exhibits strong, wide-ranging physiological effects even in minute amounts. For example, regarding the skin, estrogen has important effects including: (a) promoting blood flow; (b) improving the skin's ability to retain moisture by increasing mucopolysaccharides such as hyaluronic acid and the like; and (c) conferring elasticity to the skin by increasing elastin and collagen.
Therefore, attempts have been made to obtain an idea of the concentration of estrogen in the body. For example, there is a method in which estrogen from a tissue-derived sample obtained from serum, saliva, urine, cultured cells, or the organs is extracted with a solvent. The obtained extract is reacted with a pentahalogenated benzyl compound or a pentahalogenated benzoyl compound, and the resultant product is further reacted with 1-lower alkyl-2-halogenated pyridine. The obtained reaction mixture is then measured by LC-MS (Patent Document 1).
On the other hand, the stratum corneum is the outermost layer of the skin, and covers the cuticles. The stratum corneum has a barrier function against the intrusion of bacteria and viruses, a moisture retaining function for preventing the loss of moisture and moisturizing ingredients in the skin, and a protection function for mitigating external stimuli and the like. However, the stratum corneum is formed from “dead cells” that have lost their cell nucleus during the cornification of the skin cells. Therefore, the estrogen concentration in the stratum corneum is not measured. Rather, the estrogen concentration in the skin is measured by collecting skin tissue or blood.
Furthermore, similarly for progesterone and testosterone, which among steroid hormones are classified as sex hormones, measurement of the concentration of progesterone and testosterone in the body is usually carried out from collection of serum, saliva, urine and the like. Currently, there are no examples of measuring based on the stratum corneum.    [Patent Document 1] JP-A-2006-138786